Such systems are used, for example, as a component of painting systems. In such painting systems, the substrate surface is typically cleaned in a first step. This may be done, for example, using air pressure and/or agents for ionizing the surface, or by spraying the surface with a liquid medium, such as water or an aqueous or alcoholic or solvent-containing solution, or with a solid body, such as blasting material or CO2, or by immersing the substrates in an aqueous or alcoholic or solvent-containing solution, possibly under the influence of waves, such as ultrasound or microwaves.
When cleaning with liquid media, IR heat radiation may already be used for the following drying process.
In a second step, the actual paint layer is then applied, for example by spraying on a paint dispersion. A step follows in which the already painted substrate is baked. This can be done by means of heating with circulating air and/or by the application of infrared radiation (IR) at 50-80° C., for example. In the process, the solvent commonly present in the paint dispersion is substantially evaporated. In the case of a UV hardening paint, which is very widespread today, i.e. a paint that is cured by means of UV light, this hardening takes place in a step following the evaporation of the solvent. Depending on the application, IR and/or UV lamps are used in these process steps. In the present description, the process of drying by means of IR radiation and/or the process of curing by means of UV radiation is uniformly referred to as radiation treatment.
In order to prevent the unimpeded volatilization of the solvents into the environment or the working environment, such processes, according to the prior art, are carried out in treatment chambers. In the process, it should be ensured that a constant gas exchange takes place in order to keep the solvent concentration in the substrate environment low, for example, and to thus also accelerate the drying and/or curing process. According to the prior art, the radiation treatment is carried out in a closed chamber 1, as is schematically shown in FIG. 1. In this case, the radiation source 9, 9′, 9″ is provided in the upper part of the chamber 1 and the substrate holders 11, 11′ to be fitted with the substrates are placed in the lower part. FIG. 1 shows as substrate holders two spindles that can be fitted with components to be irradiated. The placement of the radiation sources 9, 9′, 9″ underneath the substrate holders 11, 11′ would also be possible, but is generally avoided in order not to risk the radiation sources 9, 9′, 9″ being soiled by paint residues dripping down from the substrates.
According to the prior art, an inflow region 7 is provided on the chamber ceiling, through which, supplied by an inlet 3, gas such as air, for example, flows into the chamber. According to the prior art, the gas flows past the radiation sources 9, 9′, 9″ and then the substrates 11, 11′ into the lower region of the chamber, where it is withdrawn from the chamber 1 via the outlet 5. Due to this arrangement in accordance with the prior art, the flow and gravitation cooperate in such a way that dirt, such as dust and also solvent, for example, are withdrawn effectively. In FIG. 1 the gas flow and the direction thereof is schematically illustrated by means of arrows.
However, the arrangement according to the prior art is disadvantageous in that the gas flow flowing past the substrates first has to pass the radiation sources. Generally, they are hot in operation, which results in the gas flow being heated up in an uncontrolled manner. This means that a gas flow is applied to the substrate holders 11, 11′ which has no defined temperature and in which temperature gradient may even arise across the width of the substrate holders. However, the process of drying and/or curing is heavily influenced by the prevailing temperature. Therefore, undefined temperature conditions quickly result in an uncontrolled process. Inhomogeneities may arise particularly if there are temperature gradients. The issue is exacerbated by the radiation sources themselves generally not being stabilized with regard to temperature. In the initial phase, the radiation sources will be rather cool, whereas they heat up significantly after a longer operating period. This problem could be reduced by explicit cooling measures on the radiation sources. However, such measures entail considerable technical effort and are thus expensive.
That said, it would be desirable to have a system for radiation treatment available with which the above-described issues of the prior art are ameliorated and preferably overcome entirely.
Therefore, the invention is based on the object of providing such a system.